A bobbin, which has multiple partitioning walls formed on a winding core so as to divide a winding space into multiple winding sections, is known in the art as a bobbin for manufacturing a coil of a split-winding type.
For example, as disclosed in Japanese Patent Publication No. H06-231981, a groove is formed in the partitioning wall of the bobbin so that a wire rod strides over the groove from one of winding sections to a neighboring winding section. When the wire rod is wound in one of the winding sections by a predetermined winding turns, the wire rod passes through the groove formed in the partitioning wall to the neighboring winding section.
In a general winding apparatus for a coil, a wire rod is supplied to a bobbin, which is rotated at a high speed, so that the wire rod is wound on the bobbin.
However, in a case that the wire rod is wound on the bobbin for the split-winding type coil (for example, as disclosed in the above Japanese Patent Publication No. H06-231981), the wire rod cannot surely pass through the groove formed in the partitioning wall when the bobbin is rotated at the high speed. In view of this point, in the winding apparatus of the prior art, the rotational speed of the bobbin is decreased to almost zero in order that the wire rod can pass through the groove. However, in such a winding process, it is necessary to repeat a decrease (the decrease to almost zero) and increase of the rotational speed of the bobbin each time when the wire rod passes through the groove. It requires a lot of time until the wire rod is wound on the bobbin for all of its winding sections.